Quantum dots (QDs) are a special class of nano particles with unique optical properties. They are very good candidate materials for medical and biological applications. In order to apply QDs to biological systems, they should be water soluble and bio-compatible. In this work, the water soluble CdSe(S) QDs were synthesized under hydrothermal conditions; these were then coated with a ZnO outer-shell to produce CdSe(S)/ZnO core/shell QDs in a modified literature method, resulting in QDs having better optical properties. They have been characterized by X-ray powder diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), UV-visible absorption and laser emission spectroscopy. The effects of the hydrothermal conditions and reaction time, in addition to the nature of the precursor, on the formation of the QDs were investigated.